Thermal aerodynamic drag controller



July 5; 1960 Filed Aug. 7, 1956 E. R. VAN DRIEST THERMAL AERODYNAMIC DRAG CONTROLLER 4 Sheets-Sheet 1 INVENTOR. EDWARD R. VAN DRIEST BY W M ATTORNEY July 5, 1960 E. R. VAN DRIEST 2,943,828

THERMAL AERQDYNAMIC DRAG CONTROLLER Filed Aug. 7, 1956 4 Sheets-Sheet 2 FIG. 7

0: L4 TURBULENT FLOW m l2 5 18 3 ID I'- 05 i .e ,2 E e m I 4 79 LAMINAR FLOW o |2345s1e9|o MACH NO.

fiQ-i INVENTOR.

EDWARD R. VAN DRIEST ATTORNEY July 5, 1960 E. R. VAN DRIEST 2,943,828

THERMAL AERODYNAMIC DRAG CONTROLLER Filed Aug. 7. 1956 4 Sheets-Sheet I5 FIG. I2

I INVENTOR,

EDWARD R VAN EREEST July 5, 1960 E. R. VAN DRIEST THERMAL AERODYNAMIC DRAG CONTROLLER 4 Sheets-Sheet 4 Filed Aug. 7, 1956 fig n. 7. M //w w/ m} 96 AIR FRAME STATION NO.

FREE STREAM MACH N0. M

FIG.

OUTER SURFACE RADIO COMMAND PRE PROGRAMMER FLOW RATE CONTROL TEMP SENSOR MAOH NO 37 SENSOR COOLANT INVENTOR. EDWARD R. VAN DRIEST BY fi l MU \1 ATTORNEY THERMAL AERODYNAMIC DRAG CONTROLLER Edward R. Van Driest, Whittier, Califi, assignor to North American Aviation, Inc.

Filed Aug. 7, 1956, Ser. No.602,6zs 13 Claims. or. 244-117 This invention concerns a means for decreasing aerodynamic drag upon an airframe by decreasing the temperature of the boundary layer at the surface of the'skin of the airframe. This application is a continuation-inpart of application Serial No. 327,401, filed December 22, 1952, now abandoned.

It has been discovered that when the skin of an airframe is extremely smooth and has no discontinuities, the flow, at sufiiciently low Reynolds numbers, adjacent to part of the skin is laminar and the boundary layer is said to be stabilized. When the skin of an airframe has this quality wherein the boundary layer is capable of stabilization, the boundary layer usually has three portions which, starting at the forward or front end of the airframe are a stable laminar boundary layer, an unstable laminar boundary layer, and a turbulent layer. When the temperature of the skin of the airframe is increased, the point at which the boundary layer becomes unstable and hence, the transition point between laminar and turbulent flow moves toward the forward end of the airframe, or upstream. When the temperature of the skin of an airframe is decreased, the point at which the boundary layer becomes unstable moves toward the aft end of the airframe, or downstream. At subsonic speeds, the temperature of the skin'of the airframe must be lowered by a considerable amount in order to move the position of the transition point between laminar and turbulent flow downstream by a significant amount. At supersonic speeds, a small decrease in the temperature of the skin of the airframe causes the transition point between laminar and turbulent flow to move downstream by a large amount, and when the temperature reaches a certain predetermined critical value, turbulence adjacent to the skin of the airframe is completely eliminated. At supersonic speeds it is possible to cool sufficiently to stabilize the boundary layer for all Reynolds numbers for infinitesimal disturbances. Furthermore, the-walhto-freestream temperature ratios necessary :for complete 813- bilization are attainable under practical flight conditions. A stable boundary layer adjacent to the skin of the airframe decreases the drag upon the airframe, while turbulence adjacent to the skin of the airframe increases the drag. The cooling of the airfrace skin,,be it .a fuse! lage, wing or other member, also gives structural advantages since the strength of skin materials is adversely affected by increased temperatures.

The device of this invention contemplates means for removing heat from the skin of an airframe in order to control the temperature of the boundary layer to thereby control the aerodynamic drag upon the airframe.

This invention further contemplates means for utilizing the heat energy which is removed from the skin of an airframe into a liquid heat exchange agent to drive a propulsive means which increases the thrust of the propulsion system of the airframe or drives an auxiliary power device such as an electrical generator or a fuel pump It is therefore an object of this invention to control the 2,943,828 Patented July 5,

ice

. 2 aerodynamic drag of an, airframe by controlling rheskin temperature thereof. z

It is another object of this invention to provide means for. controlling the aerodynamic dragof an airframe by controlling the skin temperature and its relationship with the free stream temperature.

It is another object of this invention to provide'means A further object of this invention is to provide means.

for removing energy fromthe boundary layer of an'airframe and converting such energy to increased thrust energy for the airframe. a

A still further object of this invention is to provide a means for moving the boundary layer transition point between laminar and turbulent flow rearwardly on an airframe skin.

Other objects of invention will become apparent from the following description .taken in connection with the accompanying drawings, in which- Fig. 1 is a half section of a typical airframe showing one embodiment of the device of this invention;

Fig. 2 is a section view taken at 2- -2 in Fig. 1;

Fig. .3 is a half section of a typical airframe showing the device of this invention adapted to preheat the fuel of the propulsion system of the airframe;

Fig. 4 is a section view takenat 4-4 in Fig. 3;

Fig. 5 is a half section view ofa typical airframe showing the device of this invention adapted to drive an auxiliary power device;

Fig. 6 shows a cross sectional view of a double walled duct with the heat inputs thereto;

Fig. 7 shows the heat inputs to a section of a preferred form of annular duct;

Fig. 8 shows graphically the heat transfer on an airframe skin as a function of Mach number;

Fig. 9 shows graphically the temperature of a fuel as a function of time at a predetermined supersonic speed;

Fig. 10 shows boundary layerconditions without heat transfer through the skin of an airframe; I

. Fig. 11 shows boundary layer conditions with a small degree of heat transfer through the airframe skin;

Fig. 12 shows the desired formof boundary layer condition with the prescribed amount ofheat transfer through the airframe skin;

Fig. 13 showsa-block diagram of a typical embodiment Fig. 14 shows graphically the neceSsaryWaH-to-freestream temperature ratio as a function of the free stream Mach number;

And Fig. 15 shows wall-to-free-stream temperatureratio as afunction of distance along an airframe skin.

' In Figs. 1 and 2 a tank 1 generally containing a fluid (liquid, gas or slurry) is connected to a pump 2 through a valve 5, the pump 2 being adapted to move the fluid within the tank 1 through a heater exchanger 4. The fluid-conducting inner structure of heat exchanger 4 is connected by a pipe 7 to an annular ductmeans 6 extending around the internal periphery of an external skin 8 of an airframe generally designated as 9. In the embodiment shown in Fig. 1 ducts 6 have one side in common with the external skin 8; ducts 6 are vented to-the outer air and may contain nozzles 52 at the rearwa-rd eridif the duct'tneans fi to provide expansion of thefluid passiug-rearwar-dly through the duct to augment the thrust of the rocket or jet or ramjet engine 50 or other device providing'the prime motive force for the airframe.

Various fluids' inay be contained in tank 5 1. "I-hes'e" include gasoline, a'JP fuel, a typical exampleiof which being a5igasohhetypehydrocarbon having approximately 20 percenf aromatics;or liquid nitrogen, 1iquid sodium, sodiu'znpotassium liquid or 'fslurr y or other fiuid' having heat exchanging capabilities. Tank l mayl-be independent of thiiough' aserie's of valves' 55 to fuel-tanks 53 which suppiythe propellantfor-the' engine 50; Control valves 55 em eentrol the -fuel i flow either direct to the engine 50 or 'bleedia p'ortion to be conducted as -a'cooiant through the ducts 6 Fuel line 56 is connected between fuel' tanksj SZs -andinjector-means (not shown) on the through pipe-24 toan auxiliary, power device 26, typically 7 aturbir'i'e'or piston type nginefwh'ich'in turndiivsfa 1 shaft or other linkage *2 8 which-niay -be 'conriectedlto' a" responder or energy utilizing device 29; "Device'29 may the fluid being used as the working fluid withinrthe prime i moverlStl, a bleed-wolf 30a may be provided from a fuel tank 30 into the liquid chamber of accumulator 31. 'In operation, heating of the skin surface due to flight condi tions 'is such that the ,fluid within the duct 21, in heat exchanging relationship with the airframe skin, 'absorbs" the skin heat and when sufiicient heat isabsorbed, tvo latilizes, and the resultant-volatiles are then conducted be any means to .do useful work driven by the fluid exit ing from the "duct. 'It'niaybe an electric generator, a

terwaid end of 'the engine 50. The heat exchangerst in=siich-conventional heat exchangers'the heat from the fluid -is taken up by the coolant, the coolant then typically being compressed, cooled by either rejecting the heat overboard or by transferring the heat to the fuel entering the tengine bypreheating,*and then'the coolant is recycled.

As hereinafter described in more detail the passage of the'coolant-ii-uidthroug'h theducts 6 acts to move the t transition'pointbetween laminar flow and turbulent'fiow rearwardly-frorna forward'station such'as the nose'stat-ion57. Fi'g. 2 is a cross sectional view taken on afor- V waremmense airframe 9 and includes partition memchanging relationship to the external skin of the 'air-' frame '1'7-acts to preheat the fuel which is passed through pipes 18' and 19 into an injector or the like associated with the prime mover'or engine 50. By reason of the passage of the fuel rexteriorly of the fuel tanks 10 and 11 the volume-of fucl'in the tanks acts as a cold'sink increasing thecoolant capabilities of the fuel as it passes through duct 16. The preheating of the fuel before it is introduced into engine 59 acts to increase engine efiiciency a's'is weilknown in'theart; 7 V

Fig 5 -'disoloses a firrther modificationof the thermal aerodynamic drag controller in'which an annular duct 21 m q'uxt'a'pos'ition withjthe inrierfiperiphery of the externa l' skin "of the airfrarne 22 extends from a forward 7 station at the nose 'of the airframe rearwardly. over the area desired to be corrected in external new characteristics; The doctor-ducts 21 in thisembodiment act as tanks for the storage of a cool fluid such as liquid nitrogen, liquid hydrogen, or Freon which acts as a skin coola'ri't; flf desired, fapr'essurc is'kcpt on the liquid within duct 21 by reason of an accumulator 31 which has a' source of pressuri'zedgaf's 23 on one side of a flexible diaseparating this gas from the liquid being fed into duct 2'1; The coolairt fluid iii certain applications may be confined entirely within the duct means 21, dispensing with a eo'olantfsu'rnp. In this event the fluid-containing source 'is withinfthe duct or adjacent ducts and the means to "flow the huidwould "typicallybe 'a means to pressurize directly as by'a'n inert gas or by reason of the inherent movement "of the volatiles through the duct means to pipe 24. When audit the 'coolantfluid is also Patent No. 2',747;0 6'4 shows the sandwich'construction of Fig. 7 "ifl'flfit8ii, HeatQ 'flowing'from th'eboundary' layer "will first enterthe outer skin 65. Part "of "the" heat 7 will"enter'thesection'69 through the outer wall and part Q will'e'nter the wanes. "Heat will then he transferred I liquid pump, an ialterina'tonla fan*blower,'or other'type of gas or hydraulic pump. By reason of the cooling of the skin surfaces the aerodynamic drag upon the exterior of the airframe 22 is substantially decreased. Exhaust gases from the turbine 'ormeans "-26 are conducted-or vented to'theannosphere through pipe 32 which is provided'with a'nozzle section '52'at the'rear end thereof to'exp'and'the waste products and to augment the-thrust of the ovrall'airframe'. In*certainapplications"the thrust emanating from nozzle section '52'issuflicient to provide the main thrust for the vehicle, thus dispensing: with all other-prime movers tsaveanexpendable booster to provide original 'startingthrirsh The basic function of the auxiliary power-device '26 is'to provide power for auxiliary devices withinthe airframe '22.

'Fig. 6'shows a cross sectional view of 'a' double annulus 7 type :ofduct which-may be embodied in the present invention. The heat Q -flowing from the boundary layer is 'transmitted'to theliquid contained between walls and 66. iPart of thisheat is'absorb'ed by the liquid and the remainder Q is transmitted through wall'6 6 to the liquid contained inrtheinner-annulus between walls 66 and 67.' Here again part of the heat is absorbed by the liquid and part Q by the wall "67 Heat from the wall 67 will be transmitted to'the liquid within'tlie inner-wall 67. In theease of theFig. 3 modification this-fluid will be in the 'fuel t-ankslfi and" 11. Reference may be had to Heat Transmission- McA'dams, W. H., McGr-aw-Hill 00., 3d ed., 1954; Thermodynamics of Fluid FlowaHail, N. -A. Prentice-Hall, like, 1951; and Elements bf Heat 'Ifransfer-Jakob, M. and Hawkins, G. A., Wiley (30., 1942, for the method of solving the necessary differential equations for the heat transferfproblem set out in the various'rnoklifications of the 'heat transfer annuli. From these equations the amount of flow of fluid can be cal cola-ted which is' nece'ssary to conduct sufiicient heat away from the skin to'insure the proper ratio of the temperature of skin to the free 'airstreaintemperature insuring l-amin'ar flow. i

i Fig, 'Z shows the heat transfer in a transverse, section of a preferred form of annulus. This fannulus not only provides good heat transfer characteristics but gives fur- V V ther'fs tre'ri'g'th to the overall airframe structure. U.Si

along the webas'wsn as to the liquids in sections 69fand 70. Heat will arrive at the "inner wall 67 via the web ssand the liquid in section 70. This heat Qi will then betraiusrnittedffrom inher wall 67 to the internal of the airframe; From the equations set out in the above-m entioned "reference books the temperature of the various walls and the quantity of heat necessary tobe transferred to insure a satisfactory wall-to-fre'e-s tream temperature ratio may be determined. v

As set out above, the boundary layer air is maintained infa state of flow thus reducing the actual heat' 7 input to the airframe and reducing the heat transfer to the exterior skin. Fig. 8 graphically demonstrates the heat problem and illustrates the advantages to be gained from a heat transfer standpoint if laminar flow is maintainer. It is to be noted thatat certain Mach numbers thatpractically a tenfold decrease may be had in heat transfer characteristic by maintaining laminar flow (curve 79) rather than turbulent flow (curve 78) In turbulent flow heat'transfer increases very rapidly with increasing Mach number as distinguished from the slower'increase as'seen' from the laminar flow curve 79. v V V Fig. 9 shows the advantage of the present invention in terms of'fuel temperature during the course of an airframe flight over finite time-intervals. In the case of turbulent flow, curve 71 illustrates a temperature increase of from about 70 F. to 400 F. in approximately four hours for a typical airframe fuel volume. If the fuel is precooled at start of flight to a value of about 50 F. the function of fuel temperature against hours will have a greater slope as is shown in curve 72, ending up with a temperature justbelow the uncooled fuel after four hours. When the airframe is flying under laminar flow conditions only a slight rise in fuel temperature is apparent illustrated in curve 73. Likewise if the fuel is 'precooled to 50 F. the fuel will retain the advantages of this precooling after over four hours flight time to a relatively high degree as seen in curve 74.

' 'Figs. 10 through 12 show diagrammatically the effect of'no heat transfer on a skin surface, a slight heat transfer from thesurface and a prescribed heat transfer on the skin surface. It can be seen that the boundary layers are suchthat the laminarflow areas 75, 76 and 77 respectively are moved to the right or rearwardly when heat is carried away from the skin surface in prescribed amounts. The upperly curving lines in each of Figs. 10 through 12 represent turbulent flow conditions and the vertical line is the point of transition between laminar and turbulent flow.

Fig. 13 is a block diagram showing a means to control the rate of flow of a fuel or other coolant through the duct means adjacent to the external skin to keep the ratio of the temperature of the skin wall-to-the-free-stream temperature at the edge of the boundary layer in a predetermined range. The block diagram in Fig. 13 combines some of the features of the modifications seen in Fig. 1, Fig. 3 and Fig. 5. Flow of the coolant fluid is commenced through the system by a pump or the like (not shown) from a tank containing the desired coolant (not shown). Control of the rate offlow is had by a flow rate controller 35. The liquid or coolant flowsv through this controller in heat exchange relationship with the airframe external skin surface 33 where it picks up heat from the boundary layer and is then conducted either through line 18 directly to the prime mover engine or alternatively is passed into a turbine 62 which is mechanically connected to a generator 60 adapted to drive a responder 29 such as a motor. Turbine 62 may drive responder 29 directly. Fluid passing through turbine 62 may be exhausted at 64 in the same direction as the main engine thrust to provide additional rearward thrust for the airframe or may be vented directly overboard. Alternatively the fluid flowing through turbine 62 may be conducted. through line 63 into a secondary heat exchanger-34 in which the picked-up heat in the fluid is transferred to a coolant loop comprised of coils 39 through which a coolant contained in a storage device 40 is passed by means of pump 45. Furthermore, straight recirculation of the fluid may be accomplished especially at times of high heat inputs. Control of flow rate may be had by providing a temperature sensor together with appropriate voltage amplifiers tov cause the rate of flow of the working substances to be dependent upon the temperature of the skin. Typically, this sensor 36 may be a thermopile or thermocouple which has a voltage output. A Mach number sensor 37, typically being a conventional Mach meter, in combination with suitable voltage amplitiers, is also adapted to forward voltage signals into the flow rate controller. Flow rate controller 35 may thus be a variable fluid valve adapted to be controlled by an electrical signal. An example of such valve may be seen in US. Patent No. 2,655,937.; The flow rate'control of 35also may be controlled by means of a radio command device 43 adapted to receive ground signals to vary valve settings or be controlledby a pre-programer 44 such' as atape recorder orkcomputer combination as is known in the valve control art. The use of the VEII'iOl IS variables set out above will become apparent from the following discussion with respect to variables effecting laminar and turbulent flow It is to be realized that the system illustrated in the above figures may also incorporate the use of intermediate working substances such as liquid metals in an outer annulus to first convey the heat from the skin of the airframe and to conduct the heat to the substancesvto be vaporized or preheated in an inner annulus. The presently described overall system may be used to provide for the skin cooling which is necessary in the re-en'try of an airframe into the atmosphere at-high speeds.

Fig. 14 illustrates the temperature ratio required for complete stabilization of the laminar boundary layer on a fiat plate. Surfaces which are slightly curved will have pressure gradients on the surface which will change the curve slightly. The area under the curve gives a stable boundary layer for all or infinite Reynolds numbers. Curve 80 is the basic curve from which a family of curves. can be drawn for lower Reynolds numbers.

The absorbtion of the boundary layer heat by the skin is.

suflicient to bring about complete stability if a prescribed temperature ratio between the wall and the free stream temperature at the edge of boundary layer T /Tt,

represented by the area under curve 80, is kept. It is to be realized that the extent to which stabilization of the boundary layer is necessary is dependent upon the particular airframe design, speed, and other variables heretofore and hereafter mentioned. Curve 82 represents the curve for an insulated plate without heat transfer. It can be seen that the amount of cooling necessary to get below curve 80 from curve 82 thus obtaining laminar flow in a Mach number range of from 1-3 is relatively small. Curves 83, 84 and 85 represent others in the family of curves mentioned above for Reynolds numbers of a million, 10,000 and 1,000 respectively. These curves may be derived theoretically or experimentally in a wind tunnel by determining the actual instability point of laminar flow under the particular flight conditions of the airframe, such as Mach number and Reynolds number. For a given Reynolds number the ratio of skin to free stream temperature at a particular Mach number must be below the corresponding curve for that Reynolds number in Fig. 14 in order to have a stabilized'boundary layer insuring laminar flow at the particular point on the external surface of the airframe skin. In some instances it might be desirable to provide the optimum control con-v ditions over only one-half the airframe surface, other areas being designed to withstand structurally and aerodystabilization and laminar flow across that airframe area. i The flow passages may be of varying size in annular cross section as the duct means extends at least partially coextensive with the skin in order to compensate for airframe contours and the varying heat inputs due to airframe shape. Further, it is generally necessary to circulate or recirculate the coolant at higher rates when the Reynolds number is increasing rapidly as at the start of ducted into the fuel and is shown by:

flight or at the necessarily; lowfbeg'inhing v ,I i w eaaa .muaaatanagrams ingthe desired 'I' /Isiratio whiehean bepre programd 'or computed dur'mf'g flight. The-equatioh fonlocal heat transfer from the boundary layer to fuel as in, Figs 3 .is

" hased'onthetotalheattrom the iboundaryflaye'r minus the ;net radiation tothe atmosphereequalstlie heat. eona tha iorthe teat heat flow zy m r T T g? dia ram t pn c nsta G h tf 'hiq' i fiiiwgoffiiel and q, specific Heat of fuel. .fsiibseriptsib,

I it; andj refe'r' to boundary layer, outer Wall, and fuel,

respectively; 7

Equations 1- and a are sank/ed, sininltane ousiy for r by successive approximations assuming various 's talnless' ste'el skin, NACA standard day, emis- B. .u. per' liqui' per square ,rdaerecev ry' v H as for laminar new in cdmp ting'the boundary layer temperatureT T6 jamrM, are calculated, from the flow field about the airframe during flight; The 'bhundary layer temperature T is computed from the renewing relationship 'ri'sj the recovery factor and 'y isthe ratio of specific heats at constant pressure" and volume;

' filthoiigh'thel inventibiihasQbeen described and illustrated in detail, it" is to he clearly understood that the samefisjbylway of'illustration and exampleonly and is no'fto' het k'enway limitation, the spirit and scope I offlthis' invention, being limited appended claims. 7

I claim: a

only by the termsof the y 11' cans tonibve the boundary layer transition point betweenlarninarflow and turbulent flow on the exterior surge-w rm airframe skin in forward flight comprising a fuel tankwithin an' airframe formed by said airframe sk in,' du ct means in contact with the interiorsurface 'of said? andextefiding re'ai vvai'dly from .forvvard portions of said'skim'a' liquid'f uel within' said tank, means withinisaid airframeto'flovvsaid fuel rearwardly through saiddu'ct means mam exchanging 'relationship with said skin =and"cont'rol means connectedto said last-mentioned means to varyith'erateiof flou of said ii-rel tokeep the ratio of the temperatureof the skin wall -to-theireer-streain temperature atthe' edge of 'the'houndary layerin ap r edetermined range, said cc'm'trol means being variable as a function of skin" temperature and 5 Mach number during said forward flight;

2: A therr'nal aerodynamic drag' controller for supersonicflight comprising an airframefhaving' an external skin,- tanks including duct means adjacent the; skin' of said'airfiame and extending rearwardly frorna predetermined station on said airframe, fluid stored Within said tanks and having a'temperature lower than saidskin during supersonic flight, pipe means connected between saidgtanks' and-the air outside of said airframe, an

auigiliary power-device connected into saidpipe means, a

responder connected to" said auxiliary power devic ff l reservoir" fuel temperatures. Other data could utiiizing'the cnergytherefi'o -.mea.ns toiflow sa'id, fromisaid tankstthrough said duc't meanstosaid devi'ee boundary layer of said airframe. andj-ahsorbszheat there- 5. froni to causerthe'pressureictsajd -fluid;to inen'ea's'eand' thereby drive sfaid auxiliaryrpoweredevice.

, 3. Inlanjairframe adapted for supersonic flighterncans mPu Y m ans cm r s s an; iprop n a n frame and said fluid is engine fuelpreheated in said duct means A a fr VT n he YPi 13$ tip cla m; prop'lsive cans comp es a duct exitingiromsaid airary thrust qutlets A 1 means to rfl'ow fluid is a pump gg, valve cnmbinatiom;

and includes sensormeans gperably connectedfio said? ssure" a consants im y of .15 3119 dduct me ns and? means t l s 5f ard.gs l a mp fluidfor driving said propulsive means.., ,,;r ;i,;;r

, i I W nqluqin aheat exchanger between said fluidgontai ning source' and said 9., The inv :tion as setqutin claim 3 duct means to precool the fluid passing into said duct means v .i r 5 0- i ra e h in an st nals ki anieansito control'the aerodynamic dragthereoninsupersonicjflight cdmprisine qg bi ia nw h a ,v air ame coolant i rc t fi's i rw w h ethasa d r r me: skin, duct means in. juxtaposition to the inte rnal surface of said skin, means ma id to saidspuree tgj flovv, coolantifluid f' b lrs r q s hmu s t isv uctmeans n at ex n t is n wi perature and Mehf i; b if f j maintaining: a; relation; ship of the ratio of said sk temperatureand the Ma number at'vaifiousReyno lds numbers as defined by the family of curves'iseen Fig.2} v 7 l2. In an airframe. havingfan Xt coolant fluid-containing sour i QWQ i FWQ Q' t rees as V. .r exchanging 'i'elationship'with the airframe skin and control of the skinextendingirearwardly fromaspredtermined e and the Mach -numbeL-Qfitthe 8. The invention as set out in clainijgin; eans t ew fl om ises; nrs sunzi r me ns to "Q BiRQ'QT PIQ. tQ' ee-s t In, a n mbfi s elqwax lu winch" isfa predetermined function of said i atio and said Mach control the aerodynamic dragthereon inrsupersgnieflight comprising in comhinationlwithlad airirame skin,, a

' w h he sa de titame skin, duct means in' juxtaposition to the internalsurf aceot;

said skin, means connected to said sguregtqn w cool nt; 7

ctmansia h at;

means to control the heat withdrawn from said skin to said fluid in an amount sufficient to stabilize the boundary layer under the particular flight conditions, said control means comprising means within said airframe skin to control the flow rate of said fluid through said duct, said control means further comprising means attached to said airframe skin for producing an electrical signal indicative of changes in skin temperature and wherein said means to control the flow rate is a flow valve responsive to said electrical signal.

13. In an airframe having an external skin, means to control the aerodynamic drag thereon in supersonic flight comprising in combination With an airframe skin, a coolant fluid-containing source within the said airframe skin, duct means in juxtaposition to the internal surface of said skin, means connected to said source to flow coolant fluid from said source through said duct means in heat exchanging relationship with the airframe skin and control means to control the heat withdrawn from said skin to said fluid in an amount sufficient to stabilize the boundary layer under the particular flight conditions, said control means comprising means Within said airframe skin to control the flow rate of said fluid through said duct, said control means further comprising means for producing an electrical signal indicative of changes in airframe speed and wherein said means to control the flow rate is a flow valve responsive to said electrical signal.

References Cited in the file of this patent UNITED STATES PATENTS 2,427,972 Melchior Sept. 23, 1947 2,529,102 Palmatier Nov. 7, 1950 2,540,594 Price Feb. 6, 1951 2,723,092 Paselk Nov. 8, 1955 FOREIGN PATENTS 435,653 France Jan. 4, 1912 612,468 Great Britain Nov. 12, 1948 687,872 Great Britain Feb. 25, 1953 

